CAMBRIAN BRACHIOPODA—WALCOTT. 325 



material was provisionally referred to 0. (Z) c(»i<-!ji/)hs^ l)ut the 

 l)roa(llv rounded subquadrilateral form of the dorsal valve seems to 

 distinguish it from that species and also from Oholns {Paleoho'x.s) 

 hrefonmsis. 



The visceral area is narrow, extending a little in advance of the 

 center of the valve. The main vascular trunks are narrow and widely 

 separated. They belong to the submarginal group and are thus quite 

 unlike those of O. (7^,) hreioncnslx. The exterior surface and ventral 

 valve are unknown. 



Formnt'ton and londlty. — Upper Cambrian. Etage 3 of Matthew, 

 McNeils Brook, 1^ miles east of Marion Bridge. Cape Breton, Nova 

 Scotia. 



OBOLUS ISMENE. new species. 



This species is characterized l)y its elevated umbo, flattened posterio- 

 lateral margins, and relatively thin shell. 



All that is known of the exterior surface indicates that it was nearly 

 smooth, marked only by tine concentric striae of growth. The inner 

 layers of the shell are beautifully marked by tine concentric and radi- 

 ating strife that give the surface a cancellated appearance. The shell 

 is built up of several layers or lamellse that become more oblique to 

 the outer surface toward the front. 



Formation and locality. — Middle Cambrian. Fotosi limestone, Flat 

 River, Missouri. 



OBOLUS MATINALIS Hall? 



Lingulepis matinalis Hall, Sixteenth Annual Report N. Y. State Cab. Nat. Hist., 

 1863, p. 130, pi. VI, figs. 12, 13. 



A form indistinguishable from this species occurs in a gray lime- 

 stone of Upper Cambrian age. Only the general form of partially 

 exfoliated shells is known. 



FoTmation and locality. — Upper Cambrian. Chao Mi Tien lime- 

 stone. Two-thirds of a mile west of Tai An Fu, Shantung, China. 



Collection of Eliot T. Blackwelder, Carnegie Institution Expedition 

 to China. 



OBOLUS MINIMUS, new species. 



This is a small shell of the general form of Ohohts shenslensls. The 

 ventral valve is obtusely accuminate and the dorsal nearly circular; 

 valves gently convex. Surface marked by rather strong concentric 

 lines of growth and numerous very line concentric stria?. The inner 

 layers of shell are shiny black and ornamented with numerous tine, 

 radiating striae and concentric lines. Shell built up of several thin 

 layers or lamellae that form a thin shell over the lambonal region that 

 gradually' thickens as the short, oblique lamella? become more numer- 

 ous toward the front and side margins. The three specimens in the 



